Experts from the Centers for Disease Control and Prevention in Atlanta recently published a paper proposing a new system of Chemical Safety Levels (CSL). Their hope is that someday the CSL system will be as widespread as the current Bio-Safety Levels (BSL) standard followed by most laboratories today.

The paper, based on a 1999 proposal by Robert Hill, Jr., Ph.D., Jean Gaunce, and Pamela Whitehead, outlines facilities and protocol requirements for chemical toxin and biotoxin research, and how these protocols differ from those for typical biocontainment labs. It also proposes a chemical hazard classification system and provides guidance on specific chemical safety practices within microbiological and biomedical laboratories.

"Biotoxins are not infectious agents, they are toxic chemicals," says Hill, acting director of the Office of Health and Safety at the CDC. "For this reason, biotoxins are subject to a whole different set of considerations for storage and handling, including very specific chemical safety precautions that are not addressed by the BSL standards."

Guidance for Labs

Hill points to two outside events that greatly influenced the decision to propose the new CSL system. The first was the adoption of the Select Agent Rule in 1996, which requires CDC inspectors to inspect labs that handle select agent toxins. Inspectors are charged with verifying that these labs comply with OSHA's laboratory regulations outlined in OSHA Standard 29, CFR 1910.1450.

About the same time, there were outbreaks in both Maryland and North Carolina of a waterborne organism called Pfiesteria piscicida. Widespread health problems were reported among people who were exposed to Pfiesteria, including fishermen, swimmers, and lab workers who tried to handle this material. These health problems involved a range of symptoms including skin and eye irritations, headaches and short-term memory loss, and respiratory distress causing asthma-type reactions.

"During this period the CDC was deluged with calls about how to deal with Pfiesteria, along with people trying to interpret the Select Agent Rule," says Hill. "Answering these calls was difficult because very often the BSL standards did not pertain if the material in question was a biotoxin."

Biotoxins, the probable causative agents in Pfiesteria, are not infectious. For this reason biotoxins are not addressed within the BSL standards even though they do require specific chemical safety precautions for both handling and storage. Each biotoxin spreads in a different manner, some create aerosols, while other are spread only through skin contact.

"Our proposed CSL system is designed to provide additional, more uniform, guidance to laboratory workers who handle hazardous chemicals," says Hill. "It is intended to merely supplement, not replace current OHSA rules, which provide general performance-based standards for labs rather than details about specific procedures."

Establishing the CSL System

In order to define the CSL system, Hill's team of researchers reviewed randomly selected laboratories to identify typical risks associated with chemical use in laboratory settings.

The team began in 2003 by evaluating approximately 20 CDC laboratories that were already taking part in CDC's annual safety survey. The safety survey is given on a rotating basis to each of the 1000 labs within the CDC.

"Although only CDC labs are being sampled to provide a basis for the CSL system, our intention is to devise a system that could be comprehensive enough to be adopted by other laboratories, not just those within the CDC system," says Hill. "We plan to continue the CSL survey process alongside of our annual safety survey."

During the initial survey phase, members of Hill's team also began reviewing the risks associated with specific chemicals. To date, more than 900 chemicals have been reviewed and designated with chemical hazard classifications that fit within four proposed CSL levels ranked 1 to 4.

Understanding the CSL Levels

Chemicals are classified by risk, including the hazardous properties of the chemical, as well as associated health hazards, flammability and reactivity. The nature of the work within the lab is also considered, including quantities being used or stored, as well as the potential for that work to cause exposure.

Low Risk (CSL-1): Any chemical risk is usually managed by restricting usage of hazardous chemicals. Typically instrument labs and equipment labs do not use hazardous chemicals openly but rather in sealed vials or containers for use inside various analytical instruments.

Moderate Risk (CSL-2): At this level, risk is still usually managed by restricting or limiting the quantities and volume of extremely hazardous chemicals allowed. This level includes laboratories that frequently use biological agents in association with various chemicals.

Substantial Risk (CSL-3): These labs typically work with a wide range of hazardous chemicals that may be, for example, very flammable, highly toxic, carcinogenic, teratogenic, or reactive. CSL-3 labs may use chemical hazard class 3 or 4 materials.

High Risk (CSL-4): The CSL-4 laboratory is a very special purpose laboratory that deals with hazardous chemicals where there is a high risk of potential exposure to highly hazardous chemicals. These laboratories might involve production or isolation of high-hazard chemicals.

Recommended Facilities Guidelines

In addition to defining the CSL levels, the CDC proposal recommends specific facility guidelines to help reduce risks associated with chemical handling and storage. General facilities guidelines include:

• Single pass air is recommended for all labs with air flow being directional into the lab. This will position the lab for future conversion if the lab's purpose changes requiring the use of single pass air.

• Laboratory-safe refrigerators are required for flammable chemical storage, since they are an important way to prevent explosions of flammable materials.

As the risk level increases, CDC's facility guidelines become more specific. For example, CSL-2 facility recommendations include a separate lab area away from desks and offices, additional security devices such as cardkeys or equivalent locks, and at minimum, biological safety cabinets. In addition, each CSL-2 laboratory supervisor should outline work practices and personal protective equipment guidelines specific to the laboratory.

At the CSL-3 level, additional facility recommendations include the use of two exit doors, laboratory hoods, vented analytical balances, and local exhaust ventilation.

"Within high risk labs, it is very important to use an enclosed analytical balance that is vented because of all the toxic chemicals in use," says Hill.

"Even though this proposal began as a research project on the side, it has captured a lot of attention since we published it," says Hill. "It may take years for an actual CSL system to become formally adopted as an industry standard, but for now we are hopeful that it will provide additional guidance to labs working with biotoxins and other hazardous materials."

The complete paper entitled "Chemical Safety Levels (CSLs): A Proposal for Chemical Safety Practices in Microbiological and Biomedical Laboratories," was originally published in Chemical Health and Safety, July/August 1999, pages 6-14, and is available through the CDC's Web site at www.cdc.gov/od/ohs/CSL%20article.htm.